Transmission system for vehicle

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transmission system for a vehicle and more particularly to an automatic transmission whose gear trains are originated from those of a conventional manual transmission.

2. Discussion of Prior Art

Generally, a manual transmission, in which the gear is manually shifted, has an input shaft directly connected to an engine and having a plurality of drive gears and has an output shaft having a plurality of driven gears paired with the drive gears and connected to drive wheels. That is, there are provided a plurality of shift gear trains between the input shaft and the output shaft. When gear is changed, after a clutch is disengaged, changeover mechanisms such as synchromesh mechanism are manually operated to change over paired shift gear trains and then the clutch is engaged. This sequence of manual operations accomplishes a gear shift of a vehicle.

The manual transmission can be converted into an automatic transmission by replacing the sequence of those manual operations with automatic operations using hydraulic actuators. This type of automatic transmission has advantages such as a small number of components, a good transmission efficiency of power and the like, compared to a conventional automatic transmission primarily constituted by planetary gears, friction engagement elements (clutches, brakes) and the like.

This type automatic transmission having a plurality of shift gear trains is-called Automated Manual Transmission (hereinafter, referred to as “AMT”). Japanese Patent Application Laid-open No. Toku-Kai 2000-55184 discloses an AMT including a main clutch (dry type clutch) for changing over the connection of a crank shaft with an input shaft between an engagement condition and a disengagement condition and a bypass clutch (hydraulically operated multiple disc clutch) for transmitting torque from the input shaft to an output shaft to prevent a so-called “torque drop”. When the main clutch changes an engagement condition, the bypass clutch is engaged by hydraulic pressure so as to prevent an abrupt drop of output torque when the gear is shifted and thus a shift shock can be alleviated.

An AMT having a bypass clutch has an advantage that an abrupt drop of output torque can be prevented by the engagement of the bypass clutch at gearshifting. Time for switching over power through the bypass clutch at gearshifting is preferably as short as possible. In particular, when the gear is up-shifted during high speed revolution of the engine, it is necessary to synchronously engage a drive gear with a driven gear and reduce the engine speed as fast as possible and as accurately as possible in order to smoothly change over gear trains doing power transmission by the changeover mechanism. That is, in order to accomplish the shift operation swiftly, it is necessary to accurately reduce the revolution of the input shaft, or the engine speed up to a synchronous revolution speed. However, it is difficult to reduce the engine speed swiftly and accurately with the bypass clutch and the engine control using the electronic control throttle valve.

Hence, Japanese Patent Application Laid-open No. Toku-Kai-Hei 4-203669 discloses a technology in which a brake is mounted on the input shaft for the purpose of preventing an over-revolution of the engine when the gear is up-shifted and a synchronizer clutch is operated when the gear is down-shifted.

However, in this technology, since a clutch is released to disconnect power transmission from the engine to the input shaft at gearshifting, particularly, when the gear is shifted from the 1^stspeed ratio to the 2^ndspeed ratio or from the 2^ndspeed ratio to the 3^rdspeed ratio, the change of driving force is so large that a shift shock can not be eliminated.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an AMT type automatic transmission system having a bypass clutch capable of changing gears swiftly and smoothly.

To achieve the object, the automatic transmission system having an input shaft, an output shaft, a plurality of drive gears mounted on the input shaft, a plurality of driven gears mounted on the output shaft and meshing with the drive gears, a torque converter disposed between a crankshaft of an engine and the input shaft, synchromesh mechanisms for synchronously engaging the drive gears with the driven gears and a shift controller for automatically actuating the synchromesh mechanisms so as to obtain a required gear ratio, comprises a lock-up clutch incorporated in the torque converter between the crankshaft and an output element of the torque converter for connecting the crankshaft with the input shaft, an electronically controlled throttle valve for automatically operating to reduce a rotation speed of the crankshaft when the gear is shifted so as to smoothly synchronize the drive gears with the driven gears, a bypass clutch for transmitting torque from the input shaft to the output shaft when the gear is shifted, while the electronically controlled throttle valve operates to reduce a rotation speed of the engine, an input clutch disposed between the output element of the torque converter and the input shaft for selectively controlling a torque transmission from the output element of the torque converter to the input shaft when the gear is shifted, and a brake mechanism disposed on an impeller shell of the torque converter for additionally reducing a rotational speed of the crankshaft while the electronically controlled throttle valve operates to reduce a rotational speed of the crankshaft so as to smoothly and swiftly engage the drive gears with the driven gears.

DESCRIPTION OF DRAWINGS

FIG. 1 is a skeleton diagram showing a transmission system for a vehicle according to a first embodiment of the present invention;

FIG. 2 is an enlarged sectional view of FIG. 1;

FIG. 3 is a block diagram showing a control circuit of a transmission system for a vehicle according to the first embodiment of the present invention;

FIG. 4 is a timing chart showing a change of torque of an output shaft versus engine speeds at an up-shift from the 1^stto 2^ndgear ratio;

FIG. 5 is a skeleton diagram showing a transmission system for a vehicle according to a second embodiment of the present invention;

FIG. 6 is a skeleton diagram showing a transmission system for a vehicle according to a third embodiment of the present invention;

FIG. 7 is an enlarged sectional view of FIG. 6;

FIG. 8 is a skeleton diagram showing a transmission system for a vehicle according to a fourth embodiment of the present invention;

FIG. 9 is a skeleton diagram showing a transmission system for a vehicle according to a fifth embodiment of the present invention;

FIG. 10 is a skeleton diagram showing a transmission system for a vehicle according to a sixth embodiment of the present invention;

FIG. 11 is an enlarged sectional view of FIG. 10;

FIG. 12 is a block diagram showing a control circuit of a transmission system for a vehicle according to the sixth embodiment of the present invention; and

FIG. 13 is a skeleton diagram showing a transmission system for a vehicle according to a seventh embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to FIG. 1, an engine <b>1</b> is provided with an electronic control throttle valve <b>2</b> for electronically controlling engine torque and engine speeds. Normally, the electronic control throttle valve <b>2</b> is opened and closed by output signals from an electronic control unit (not shown) according to the amount of depression of an accelerator pedal (not shown) to control the engine <b>1</b>. Further, when needed, the electronic control throttle valve <b>2</b> can be opened and closed to control the engine <b>1</b> based on a preestablished table irrespective of the amount of depression of the accelerator pedal.

Further, a transmission system for transmitting power of the engine <b>1</b> to driving wheels is exemplified as a transmission system used for a four wheel drive vehicle in this embodiment. The transmission system is mounted on a vehicle in a longitudinal direction thereof and has an input shaft <b>3</b> connected to the engine and an output shaft <b>4</b> connected to driving wheels and disposed in parallel with the input shaft. These input and output shafts are arranged in a longitudinal direction of the vehicle in a transmission case <b>5</b>. The input shaft <b>3</b> is connected through a torque converter <b>6</b> to a crank shaft <b>7</b> of the engine <b>1</b>.

Drive gears <b>11</b>, <b>12</b> for the 1^stgear ratio and the 2^ndgear ratio respectively are fixed to the input shaft <b>3</b> and further drive gears <b>13</b>, <b>14</b> and <b>15</b> for the 3^rd, 4^thand 5^thgear ratios respectively are rotatably mounted on the input shaft <b>3</b>. Further, driven gears <b>21</b>, <b>22</b> for the 1^stand 2^ndgear ratios respectively are rotatably mounted on the output shaft <b>4</b> and driven gears <b>23</b>, <b>24</b> and <b>25</b> for the 3^rd, 4^thand 5^thgear ratios respectively are fixed to the output shaft <b>4</b>. Respective drive gears <b>11</b> to <b>15</b> mesh with respective driven gears <b>21</b> to <b>25</b> to form respective shift gear trains. The gear is shifted by changing over the shift gear trains. Further, a drive gear <b>16</b> for reverse speed is secured to the input shaft <b>1</b>.

The output shaft <b>4</b> is provided with a first synchromesh mechanism <b>31</b> between the driven gear <b>21</b> for the 1^stgear ratio and the driven gear <b>22</b> for the 2^ndgear ratio. The input shaft <b>3</b> is provided with a second synchromesh mechanism <b>32</b> between the drive gear <b>33</b> for the 3^rdgear ratio and the drive gear <b>14</b> for the 4^thgear ratio and a third synchromesh mechanism <b>33</b> adjacent the drive gear <b>15</b> for the 5^thgear ratio.

The synchromesh mechanism <b>31</b> includes a synchronizer hub <b>31</b><i>a </i>secured to the output shaft <b>2</b> and a synchronizer sleeve <b>31</b><i>b </i>constantly meshing with the synchronizer hub <b>31</b><i>a</i>. When the synchronizer sleeve <b>31</b><i>b </i>meshes with a spline <b>21</b><i>a </i>integrally formed with the driven gear <b>21</b> for the 1^stgear ratio, the gear ratio is established to the 1^stgear ratio and when the synchronizer sleeve <b>31</b><i>b </i>meshes with a spline <b>22</b><i>a </i>integrally formed with the driven gear <b>22</b> for the 2^ndgear ratio, the gear ratio is established to the 2^ndgear ratio.

Other synchromesh mechanisms <b>32</b>, <b>33</b> include synchronizer hubs <b>32</b><i>a</i>, <b>33</b><i>a </i>secured to the input shaft <b>1</b> and synchronizer sleeves <b>32</b><i>b</i>, <b>33</b><i>b </i>constantly meshing with the synchronizer hubs <b>32</b><i>a</i>, <b>33</b><i>a</i>, respectively. When these synchronizer sleeves <b>32</b><i>b</i>, <b>33</b><i>b </i>are engaged with either of the corresponding splines <b>13</b><i>a</i>, <b>14</b><i>a </i>and <b>15</b><i>a</i>, the gear ratio is established to either of the 3^rdto 5^thgear ratios.

The traveling in an axial direction and engagement with the splines <b>21</b><i>a</i>, <b>22</b><i>a</i>, <b>13</b><i>a</i>, <b>14</b><i>a </i>and <b>15</b><i>a </i>of the respective synchronizer sleeves <b>31</b><i>b</i>, <b>32</b><i>b </i>and <b>33</b><i>b </i>is performed by a hydraulic actuator (not shown).

The synchronizer sleeve <b>31</b><i>b </i>of the first synchromesh mechanism <b>31</b> is provided with a driven gear <b>26</b> for reverse speed. Further, an idler gear (not shown) is slidably mounted on an idler shaft (not shown) in parallel with the input and output shafts <b>3</b>, <b>4</b> respectively so as to axially travel between positions where the reverse driving gear <b>16</b> is engaged and disengaged with the driven gear <b>26</b>. Accordingly, when the idler gear travels to mesh with the reverse drive gear <b>16</b> and the reverse driven gear <b>26</b> while the synchronizer sleeve <b>31</b><i>b </i>is a neutral position, the output shaft <b>4</b> rotates in a reverse direction.

The output shaft <b>4</b> is hollowed around the center thereof and a front wheel output shaft <b>34</b> is incorporated in the hollow. The output shaft <b>4</b> is connected with the front wheel output shaft <b>34</b> through a center differential <b>35</b> and the front wheel output shaft <b>34</b> is connected with a front wheel drive shaft (not shown) through a front differential <b>36</b>. Further, the center differential <b>35</b> is connected with a rear wheel output shaft <b>39</b> through a drive gear <b>37</b> and a driven gear <b>38</b> and the rear output shaft <b>39</b> is connected with a rear wheel drive shaft (not shown) through a rear differential (not shown).

A bypass gear <b>17</b> of the drive side is rotatably mounted on the input shaft <b>3</b> and a bypass gear <b>27</b> of the driven side is secured to the output shaft <b>4</b>. These gears <b>17</b>, <b>27</b> are constantly in a meshing condition. The input shaft <b>3</b> is provided with a bypass clutch <b>18</b> which comprises a clutch hub <b>20</b> fixed to the input shaft <b>3</b> and a clutch drum <b>19</b> fixed to the bypass gear <b>17</b>. The clutch drum <b>19</b> is provided with a plurality of clutch discs of the drive side and the clutch hub <b>20</b> is provided with a plurality of clutch discs of the driven side. The clutch discs of the drive side are disposed in interleaving relation to the clutch discs of the driven side. Power of the input shaft <b>3</b> is transmitted to the output shaft <b>4</b> through the bypass clutch <b>18</b> by pressing those clutch discs by means of hydraulic pressure in an axial direction. When releasing those clutch discs, power transmission is disconnected between the input shaft <b>3</b> and the output shaft <b>4</b>.

As shown in FIG. 2, the torque converter <b>6</b> has a pump side outer shell <b>42</b> including a pump impeller <b>41</b> and a front cover <b>43</b> secured to the outer shell <b>42</b>. The front cover <b>43</b> is secured to a drive plate <b>44</b> integrally connected with the crankshaft <b>7</b>. A turbine runner <b>45</b> disposed opposite to the pump impeller <b>41</b> is directly connected with a turbine shaft <b>46</b> through a spline. The turbine shaft <b>46</b> is rotatably incorporated in a hollow supporting shaft <b>47</b> and a stator <b>49</b> is provided on the supporting shaft <b>47</b> through an one-way clutch <b>48</b>. The pump side outer shell <b>42</b> and front cover <b>43</b> are an input element of the torque converter <b>6</b> respectively and the turbine runner <b>45</b> and turbine shaft <b>46</b> are an output element of the torque converter <b>6</b> respectively.

A lock-up clutch <b>51</b> is fitted over the turbine shaft <b>46</b> in such a manner that power can be transmitted when the lock-up clutch <b>51</b> is pressed on the front cover <b>43</b>. There is provided an apply chamber <b>51</b><i>a </i>to which hydraulic pressure is fed to press the loch-up clutch <b>51</b> on the front cover <b>43</b> on one side of the lock-up clutch <b>51</b> and there is provided a release chamber <b>51</b><i>b </i>from which hydraulic pressure is released to disengage the lock-up clutch <b>51</b> on the other side thereof. When hydraulic pressure is fed to the release chamber <b>51</b><i>b </i>and is circulated through the apply chamber <b>51</b><i>a</i>, the lock-up clutch <b>51</b> is released and the torque converter <b>6</b> is operative. On the other hand, when hydraulic pressure is fed to the apply chamber <b>51</b><i>a </i>and hydraulic pressure in the release chamber <b>51</b><i>b </i>is reduced, a clutch disc <b>52</b> of the lock-up clutch <b>51</b> is pressed by the front cover <b>43</b> to produce a lock-up condition. The lock-up clutch <b>51</b> is engaged when vehicle speed exceeds a specified value based on a table parameterizing vehicle speeds and accelerator pedal opening angles. Thus, power of the crankshaft <b>7</b> is transmitted to the turbine shaft <b>46</b> through the torque converter <b>6</b> or the lock-up clutch <b>51</b>.

There is provided an input clutch <b>53</b> between the turbine shaft <b>46</b> and the input shaft <b>3</b>. The input clutch <b>53</b> comprises a clutch drum <b>54</b> fixed to the turbine shaft <b>46</b> and a clutch hub <b>55</b> secured to the input shaft <b>3</b> through a spline. When a clutch drive disc <b>54</b><i>a </i>mounted on the clutch drum <b>54</b> is engaged with a clutch driven disc <b>55</b><i>a </i>mounted on the clutch hub <b>55</b>, the turbine shaft <b>46</b> is connected with the input shaft <b>3</b>. When the engagement is released, the turbine shaft <b>46</b> is disconnected from the input shaft <b>3</b>.

As shown in FIG. 2, a clutch piston <b>56</b> is mounted in the clutch drum <b>54</b>. When hydraulic pressure is supplied to an oil chamber <b>56</b><i>a</i>, the clutch drive disc <b>54</b><i>a </i>is engaged with the clutch driven disc <b>55</b><i>a </i>and when hydraulic pressure is stopped to be supplied, the engagement is released by the spring force of spring member <b>57</b>.

An oil pump <b>59</b> is incorporated in a supporting wall <b>58</b> connected with the transmission case <b>5</b>. A rotor of the oil pump <b>59</b> is driveably connected with an extension member of the pump side outer shell <b>42</b> of the torque converter <b>6</b> and is driven by the crankshaft <b>7</b> through the pump side outer shell <b>42</b>. Hydraulic fluid discharged from the oil pump <b>59</b> is supplied to the torque converter <b>6</b>, the bypass clutch <b>18</b>, the input clutch <b>53</b>, hydraulically operated devices such as the aforesaid hydraulic actuators and lubricating parts after being converted into a hydraulic fluid with a specified hydraulic pressure for each device.

There is provided a brake mechanism <b>61</b> outside of the outer shell <b>42</b> on the pump side. The brake mechanism <b>61</b> has a brake disc <b>82</b> secured to the outer shell <b>42</b> and a caliper <b>63</b> for braking the brake disc <b>62</b> by clamping the disc in between. The caliper <b>63</b> is mounted on the transmission case <b>5</b>.

As shown in FIG. 2, the caliper <b>63</b> is mounted on a caliper body <b>64</b> secured to the transmission case <b>5</b>. The caliper body <b>64</b> includes two hydraulic cylinders <b>65</b><i>a </i>and <b>65</b><i>b </i>which are provided opposite to each other. The respective hydraulic cylinders <b>65</b><i>a</i>, <b>65</b><i>b </i>have hydraulic pistons <b>66</b><i>a</i>, <b>66</b><i>b </i>on which brake pads <b>67</b><i>a</i>, <b>67</b><i>b </i>are installed respectively so as to interleave the brake disc <b>62</b>.

Accordingly, when working fluid is supplied to the respective hydraulic cylinders <b>65</b><i>a</i>, <b>65</b><i>b </i>in accordance with vehicle operating conditions, the brake disc <b>62</b> contacts the brake pads <b>67</b><i>a</i>, <b>67</b><i>b </i>to reduce the rotation speed of the crankshaft <b>7</b>. For example, when the brake mechanism <b>61</b> is operated at an up-shift, since the electronic control throttle valve <b>2</b> additionally reduces the engine speed, the rotation speed of the crankshaft <b>7</b> descends to a specified value for a very short time. As a result, the shift operation can be performed smoothly and swiftly. Further, since a braking force is applied to the crankshaft <b>7</b> at a radially remote place on the outer shell <b>42</b> of the torque converter <b>6</b>, a large braking force can be obtained without applying a large pressing force on the brake pads <b>67</b><i>a</i>, <b>67</b><i>b. </i>

Referring to FIG. 3, a shift controller <b>70</b> inputs a rotational speed of the crankshaft <b>7</b> from an engine speed sensor <b>71</b>, a throttle valve opening angle from a throttle valve opening angle sensor <b>72</b>, a traveling speed of a vehicle from a vehicle speed sensor <b>73</b>, a range of the automatic transmission like drive range, neutral range from an inhibitor switch <b>74</b> and a brake signal indicative of an abrupt braking from a brake sensor <b>75</b> by detecting a depression amount of a brake pedal.

The bypass clutch <b>18</b>, the lock-up clutch <b>51</b> and the input clutch <b>53</b> are actuated by means of hydraulic pressure regulated by electromagnetic valves provided in a valve control unit <b>76</b>. The valve control unit <b>76</b> is controlled by signals from the shift controller <b>70</b>. Further, the synchronizer sleeves <b>31</b><i>b</i>, <b>32</b><i>b </i>and <b>33</b><i>b </i>are actuated for engagement in the axial direction by a plurality of hydraulic actuators <b>77</b>. Regulated hydraulic pressure is supplied to the respective actuators <b>77</b> from the electromagnetic valves provided in the valve control unit <b>76</b>. The shift controller has a memory in which a shift table parameterizing throttle opening angles, vehicle speeds and the like is stored so as to automatically perform a shift operation by detecting actual engine speeds, accelerator pedal opening angles, vehicle speeds, rotation speed of the output shaft, gear positions and the like.

When a selector lever provided in the passenger compartment is positioned at a neutral range under an engine operative condition, both lock-up clutch <b>71</b> and input clutch <b>73</b> are established in a released condition.

When the selector lever selects a forward drive range, since the selector lever is interlocked with one of manual valves (not shown) of a hydraulic control mechanism incorporated in the transmission system, the input clutch <b>53</b> is engaged by hydraulic pressure supplied thereto. At this moment, there is a sequence to operate the input clutch <b>53</b>. First, an hydraulic actuator slides the synchronizer sleeve <b>31</b><i>b </i>and engages it with the spline <b>21</b><i>a </i>to place this shift gear train for the 1^stgear ratio in a power transmitting condition. After that, hydraulic pressure is supplied so as to engage the input clutch <b>53</b>. Thus, engine power is transmitted to the input shaft <b>3</b> through the torque converter <b>6</b> and the input clutch <b>53</b> to drive the vehicle. Then, engine torque transmitted to the input shaft <b>3</b> is amplified by the torque converter <b>6</b>.

As the accelerator pedal opening angle increases, the electronic control throttle valve <b>2</b> operates and up-shifts are performed. When the vehicle speed goes down or when the accelerator pedal is suddenly depressed (kick down), down-shifts are performed. The gear is shifted automatically according to shift schedules programmed in a shift control section.

At up-shifting, while the input clutch <b>53</b> is retained in such a condition as being able to variably transmit torque according to vehicle operating conditions, the bypass clutch <b>18</b> starts to be engaged and then is controlled so as to gradually increase the transmission torque of the bypass clutch <b>18</b>. For example, the engine speed is reduced to a specified value corresponding to the 2^ndgear ratio by controlling the electronic control valve <b>2</b> to synchronize and engage the synchronizer sleeve <b>31</b><i>b </i>with the spline <b>22</b><i>a </i>of the driven gear <b>22</b> of 2^ndgear ratio. At this moment, when the gear is changed, power is transmitted from the input shaft <b>3</b> to the output shaft <b>4</b> through the bypass gears <b>17</b> and <b>27</b> due to the engagement of the bypass clutch <b>18</b> without shutting off power of the engine and as a result torque drops can be eliminated at gearshifting.

The input shaft <b>3</b> can be synchronously engaged with the output shaft <b>4</b> through the bypass clutch <b>18</b>, while a torque drop between the input shaft <b>3</b> and the output shaft <b>4</b> is prevented. Further, when the gear is up-shifted, since the rotation speed of the input shaft <b>3</b> can be reduced in short time with accuracy to a specified number of revolution by simultaneously operating both the brake mechanism <b>61</b> and the electronic control throttle valve <b>2</b>, fast synchronous engagements are obtained when the gear trains steps from a low speed stage to a high speed stage. On the other hand, when the gear is down-shifted, since the engine speed can be raised by the control of the electronic control throttle valve <b>2</b>, the input shaft <b>3</b> can be synchronously and smoothly engaged with the output shaft <b>4</b>.

When the vehicle starts, the input clutch <b>53</b> is in an engaged condition. Further, when the vehicle travels, the input clutch <b>53</b> is also in an engaged condition. When the gear is down-shifted, if the input clutch <b>53</b> stays in an engaged condition, drag torque retains engine speed in a reduced condition. Hence, at down-shifting, the input clutch <b>53</b> is controlled so as to be partially engaged, that is, in a slip condition and as a result it becomes possible to increase the engine speed at down-shifting.

For example, when the vehicle travels at low or medium speed under a high speed stage such as the 4^thor 5^thspeeds, the riding comfort is exacerbated due to the effect of torque fluctuation at low engine speeds. Under these traveling conditions, when the input clutch <b>53</b> is engaged in a minimum torque transmission condition, the input clutch <b>53</b> acts as a dumper and the torque fluctuation is prevented from being transmitted to a vehicle drive train. As a result, the riding comfort is prevented from being exacerbated.

Since the lock-up clutch <b>51</b> is incorporated in the torque converter <b>6</b>, in order to supply hydraulic pressure from an electromagnetic valve provided in the valve control unit <b>76</b> to the lock-up clutch <b>51</b>, a long oil delivery path is required. Further, since the lock-up clutch <b>51</b> is operated by a pressure difference between the apply chamber <b>51</b><i>a </i>and the release chamber <b>51</b><i>b</i>, in case where oil temperature is low, it takes a long time <b>14</b> for the lock-up clutch <b>51</b> to change over from an engaged condition to a released condition due to the effect of viscosity of working fluid. As a result, when the engine speed goes down while the engine is connected with the input shaft <b>3</b>, engine stalls may occur.

On the other hand, the input clutch <b>53</b> is designed such that when hydraulic pressure is supplied to the oil chamber <b>56</b><i>a</i>, the input clutch <b>53</b> is engaged and when oil is discharged from the oil chamber <b>56</b><i>a</i>, the input clutch <b>53</b> is released. Furthermore, since the input clutch <b>53</b> is disposed in a place close to an electromagnetic valve provided in the valve control unit <b>76</b>, the oil delivery path from the electromagnetic valve to the input clutch <b>53</b> is shorter than that from the electromagnetic valve to the lock-up clutch <b>51</b> and as a result the input clutch <b>53</b> has a better responsibility than the lock-up clutch <b>51</b>. Therefore, when abrupt braking is applied, the input clutch <b>53</b> is released while the lock-up clutch <b>51</b> is engaged. As a result, when the engine speed goes down abruptly, engine stalls can be prevented.

FIG. 4 is a timing chart showing a time-versus change of a torque To of the output shaft <b>4</b> and a time-versus change of an engine speed Ne when the gear is up-shifted from the 1^stto 2^ndgear ratio.

In the drawing, a shift position indicates a position of the synchronizer sleeve <b>31</b><i>b</i>. That is, the state “1^stspeed” indicates that the synchronizer sleeve <b>31</b><i>b </i>is engaged with the driven gear <b>21</b> through the spline <b>21</b><i>a</i>, the state “Neutral” indicates that the synchronizer sleeve <b>31</b><i>b </i>is disengaged from the spline <b>21</b><i>a</i>, and the state “2^ndspeed” indicates that the synchronizer sleeve <b>31</b><i>b </i>is engaged with the driven gear <b>22</b> through the spline <b>22</b><i>a. </i>

In a power delivery path “1^stgear train”, engine power is transmitted to the output shaft only through the 1^stspeed gear train and in a power delivery path “Phase I”, engine power is transmitted to the output shaft through both the 1^stspeed gear train and the bypass clutch <b>18</b>. In a power delivery path “Phase II”, engine power is transmitted only through the bypass clutch <b>18</b>. Further, in a power delivery path “Phase III”, power is transmitted through both the 2^ndspeed gear train and the bypass clutch <b>18</b> and in a power delivery path “2^ndgear train”, engine power is transmitted only through the 2^ndspeed gear train.

When a gear shift is performed, first, hydraulic pressure is supplied to the bypass clutch <b>18</b>, a condition where power is transmitted through the 1^stspeed gear train formed by the drive gear <b>11</b> and the driven gear <b>21</b> changes to a condition of Phase I where power is transmitted through two power delivery paths, the 1^stspeed gear train and the gear train of the bypass gears <b>17</b> and <b>27</b>.

Since the drive gear <b>11</b> of the 1^stgear ratio driveably meshes with the driven gear <b>21</b> and on the other hand the bypass gear <b>17</b> drives the bypass gear <b>27</b>, the bypass gear <b>17</b> rotates at a higher speed than the drive gear <b>11</b> due to the difference of gear ratios. As a result, torque is transmitted through the gear train of the bypass gears <b>17</b>, <b>27</b> according to the engagement condition of the bypass clutch <b>18</b>.

Next, the synchronizer sleeve <b>31</b><i>b </i>transfers to a neutral position, namely the Phase II condition, in which the synchronizer sleeve <b>31</b><i>b </i>meshes only with the synchronizer hub <b>31</b><i>a</i>. Under the condition, power is transmitted from the input shaft <b>3</b> to the output shaft <b>4</b> through the gear train of the bypass gears <b>17</b>, <b>27</b> and at the same time the rotational speed of the input shaft <b>3</b> is reduced by the closing operation of the electronic control throttle valve <b>2</b> to synchronize the input shaft <b>3</b> with the output shaft <b>4</b>. At this moment, the brake mechanism <b>61</b> operates to brake the crankshaft <b>7</b> and as a result time for synchronizing can be shortened.

When the engine rotational speed is reduced to a level corresponding to the 2^ndspeed, a condition where the synchronizer sleeve <b>31</b><i>b </i>meshes only with the synchronizer hub <b>31</b><i>a </i>transfers to a condition where the synchronizer sleeve <b>31</b><i>b </i>meshes with the spline <b>22</b><i>a</i>. As a result, in this condition, Phase III condition, the power delivery path has two paths, one is a shift gear train of the 2^ndspeed and another is a gear train of the bypass gears <b>17</b>, <b>27</b>. When the synchronizer sleeve <b>31</b><i>b </i>comes into a meshing condition with the spline <b>22</b><i>a</i>, the braking torque of the brake mechanism <b>61</b> is released and no braking force is applied to the crankshaft <b>7</b>.

Under the Phase III condition, when hydraulic pressure fed to the bypass clutch <b>18</b> is drained to release the bypass clutch <b>18</b>, an up-shift to the 2^ndspeed is accomplished and then power is transmitted from the input shaft <b>3</b> to the output shaft <b>4</b> through the gear train of the 2^rdspeed.

Thus, the bypass clutch control and the engine control are performed simultaneously and when the rotational speed of the engine is reduced to a speed corresponding to the 2^ndspeed, the synchronizer sleeve <b>31</b><i>b </i>meshes with the spline <b>22</b><i>a</i>. As a result, no gear clash occurs and the shift operation can be accomplished smoothly. Further, when the synchronizer sleeve <b>31</b><i>b </i>is at a neutral position, since power is transmitted through the bypass clutch <b>18</b>, so-called “torque drop” can be reduced. Particularly, the torque drop becomes noticeable when the gear is up-shifted from the 1^stspeed to the 2^ndspeed or from the 2^ndspeed to the 3^rdspeed.

Referring to FIG. 4, two-dots chain lines indicate a change of engine speeds when the brake mechanism <b>61</b> is inoperative and solid lines indicate a change of engine speeds when the brake mechanism <b>61</b> is operative. As understood from the difference of these changes, when the brake mechanism <b>61</b> is operative, since time for transmitting power from the input shaft <b>3</b> to the output shaft <b>4</b> only through the bypass clutch <b>18</b>, that is, time in the Phase II condition can be shortened surely and accurately, the total time for gearshifting can be shortened.

FIG. 4 shows a change of engine speeds and torque when the gear is up-shifted from the 1^stto 2^ndgear ratio. Other up-shift operations such as an operation from the 2^ndto 3^rdgear ratios and the like are done in a similar manner. As understood from FIG. 4, a gearshift operation at up-shifting can be done swiftly. In case where the gear ratio of the bypass gears <b>17</b>, <b>27</b> of the bypass clutch <b>18</b> is selected to a value corresponding to that of the 4^thspeed, when the gear is up-shifted to high speed stages such as from the 4^thspeed to the 5^thspeed, the gear may be shifted without involving the bypass clutch <b>18</b> (with the bypass clutch <b>18</b> released), because the gear ratio of the bypass gears is near to that of the 4^thspeed and accordingly the drop of driving force is small.

On the other hand, when the gear is down-shifted, since the drop of output torque is not so noticeable, the input clutch <b>53</b> may be operated to shut off power transmission to the input shaft <b>3</b>. Further, also when the gear is down-shifted, the bypass clutch <b>18</b> may be engaged so as to change over the control between power deliveries through two paths and power transmission only through the bypass clutch <b>18</b> while the engine control and the brake control by the brake mechanism <b>61</b> are performed.

FIG. 5 is a skeleton diagram showing a transmission system according to a second embodiment of the present invention. The components identical to the first embodiment are denoted by identical reference numbers and are not described in detail.

In this transmission system, the brake mechanism <b>61</b> is provided on an outer side of the clutch drum <b>54</b> of the input clutch <b>53</b>. A plurality of spline grooves <b>81</b> having grooves in an axial direction are circumferentially formed integrally with the transmission case <b>5</b> and a plurality of driven discs <b>81</b><i>a </i>are fitted to the spline grooves <b>81</b>. Further, a plurality of drive discs <b>54</b><i>b </i>are driveably mounted on spline teeth formed on the outer side of the clutch drum <b>54</b>. The drive discs <b>54</b><i>b </i>contact the driven discs <b>81</b><i>a </i>in an interleaving manner with each other. When hydraulic pressure is applied to these drive discs <b>54</b><i>b </i>and the driven discs <b>81</b><i>a</i>, an engagement force generates between these discs. Brake torque of the brake mechanism <b>61</b> is regulated by adjusting the engagement force with hydraulic pressure. As shown in FIG. 5, since components of the brake mechanism <b>61</b> is coaxially formed on an outer periphery of the clutch drum <b>54</b> of the input clutch <b>53</b>, the axial length of the-transmission system can be shortened. In order to smoothly control the rotation of the crankshaft <b>7</b> of the transmission system, the brake mechanism <b>61</b> is operated while the lock-up clutch <b>51</b> which is directly connected with the crankshaft <b>7</b> is engaged. Thus, since the input clutch <b>53</b> is driveably connected with the crankshaft <b>7</b>, engine power can be directly transmitted to the input shaft <b>3</b> by engaging the input clutch <b>53</b>. As a result, the gear can be shifted smoothly and fuel economy in medium to high speed ranges can be enhanced due to very small loss of power transmission.

In case of the transmission system of a third embodiment shown in FIG. <b>6</b> and FIG. 7, the brake mechanism <b>61</b> is disposed between the stator <b>49</b> of the torque converter <b>6</b> and the supporting shaft <b>47</b> for supporting a reaction torque of the stator <b>49</b>. The brake mechanism <b>61</b> includes a brake drum <b>82</b> secured to the supporting shaft <b>47</b> through spline fitting and a brake hub <b>83</b> fixed to the pump side outer shell <b>42</b>. Brake driven discs <b>82</b><i>a </i>are mounted on the brake drum <b>82</b> and brake drive discs <b>83</b><i>a </i>are driveably mounted on the brake hub <b>83</b>. Further, the brake driven discs <b>82</b><i>a </i>have contact with the brake drive discs <b>83</b><i>a. </i>

A brake piston <b>84</b> is slidably incorporated in the brake drum <b>82</b>. When working fluid is fed to an oil chamber <b>84</b><i>a</i>, the brake discs <b>82</b><i>a </i>and <b>83</b><i>a </i>generate an engagement force. Braking torque of the brake mechanism <b>61</b> is regulated by adjusting the engagement force of the brake discs <b>82</b><i>a</i>, <b>83</b><i>a</i>. The brake piston <b>84</b> is subjected to a biasing force in a releasing direction by a spring member <b>85</b>.

In this transmission system, since the brake mechanism <b>61</b> is disposed inside of the stator <b>49</b> of the torque converter <b>6</b>, the axial or longitudinal size of the transmission system can be shortened. As a result, the transmission system can be introduced into a variety of types of transmission.

FIG. 8 is a skeleton diagram showing a transmission system according to a fourth embodiment. In this transmission system, the brake mechanism <b>61</b> is formed between the pump side outer shell <b>42</b> of the torque converter <b>6</b> and the transmission case in the same manner as in the first embodiment. On the other hand, the lock-up clutch <b>51</b> is driveably connected with the input shaft <b>3</b>. When the lock-up clutch <b>51</b> is engaged, the crankshaft <b>7</b> is directly connected with the input shaft <b>3</b>. The input clutch <b>53</b> is incorporated between the turbine runner <b>45</b> of an output element of the torque converter <b>6</b> and the lock-up clutch <b>51</b>.

The input clutch <b>53</b> comprises a clutch drum <b>54</b> fixed to the turbine runner <b>45</b>, a clutch drive disc <b>54</b><i>a </i>mounted on the clutch drum <b>54</b>, a clutch hub <b>55</b> which is connected to the input shaft <b>3</b> and a clutch driven disc <b>55</b><i>a </i>mounted on the clutch hub <b>55</b>. The rotation of the turbine runner <b>45</b> is transmitted to the input shaft <b>3</b> through the input clutch <b>53</b>. Accordingly, in case where the input clutch <b>53</b> is disengaged and the lock-up clutch <b>51</b> is engaged, or in case where the input clutch <b>53</b> is engaged and the lock-up clutch <b>51</b> is released, the rotation of the crankshaft <b>7</b> is directly transferred to the input shaft <b>3</b>.

FIG. 9 is a skeleton diagram showing a fifth embodiment of a transmission system.

In this transmission system, the input clutch <b>53</b> is disposed between an output element of the turbine runner <b>45</b> and an input element of the lock-up clutch <b>51</b> in the same manner as in case of FIG. <b>8</b> and the brake mechanism <b>61</b> is provided on an inner periphery surface of the stator <b>49</b> of the torque converter <b>6</b>.

In these transmission systems shown in FIG. <b>8</b> and FIG. 9, since the input clutch <b>53</b> and the lock-up clutch <b>51</b> are integrally incorporated in the torque converter <b>6</b> and the clutch drum of the input clutch <b>53</b> is driveably connected with the turbine runner <b>45</b>, the axial or length of the transmission system can be shortened. As a result, a variety of transmission types, transversely mounted type, longitudinally mounted type and the like, can introduce these transmission systems.

The transmission systems described before in the second, third, fourth and fifth embodiments have automatic transmissions comprising the torque converter <b>6</b>, the input clutch <b>53</b>, the brake mechanism <b>61</b>, a plurality of shift gear trains and the bypass clutch <b>18</b> for transmitting torque from the input shaft <b>3</b> to the output shaft <b>4</b> when needed. These transmission systems perform similar shift operations to the transmission system described in the first embodiment.

FIG. 10 shows a transmission system according to a sixth embodiment. The transmission system comprises a flywheel dumper <b>90</b>, an input clutch <b>53</b>, a brake mechanism <b>61</b>, a plurality of shift gear trains and a bypass clutch <b>18</b>, not including a torque converter.

As shown in FIG. <b>10</b> and FIG. 11, the flywheel dumper <b>90</b> comprises a drive plate <b>91</b> driveably secured to the crankshaft <b>7</b> and a driven plate <b>93</b> connected with the drive plate through a spring member <b>92</b> for absorbing shocks. The driven plate is spline-fitted over a rotation shaft <b>94</b> which is rotatably supported by the supporting wall <b>58</b> of the transmission case <b>5</b>.

The input clutch <b>53</b> includes the clutch drum <b>54</b> secured to the rotation shaft <b>94</b> and the clutch hub <b>55</b> secured to the input shaft <b>3</b>. Similarly to the first embodiment, there are provided clutch drive discs <b>54</b><i>a </i>and clutch driven discs <b>55</b><i>a </i>interleaving relationship with each other between the clutch drum <b>54</b> and the clutch hub <b>55</b>. When hydraulic pressure is supplied to the oil chamber <b>56</b><i>a</i>, the clutch piston <b>56</b> presses the clutch discs <b>54</b><i>a</i>, <b>55</b><i>a </i>and as a result an engagement force generates between the clutch discs <b>54</b><i>a</i>, <b>55</b><i>a</i>, thus the input clutch <b>53</b> being engaged. Further, according to the magnitude of hydraulic pressure applied to the oil chamber <b>56</b><i>a</i>, the input clutch <b>53</b> can retained in any conditions from a partially engaged or slip condition to a fully engaged condition. When hydraulic pressure is stopped to be supplied to the oil chamber <b>56</b><i>a</i>, the engagement force is lost by the spring member <b>57</b>, the input clutch <b>53</b> being released.

With respect to the brake mechanism, the brake disc <b>62</b> is fixed to an extension member of the drive plate <b>91</b>. Accordingly, the brake disc <b>62</b> is directly connected with the crankshaft <b>7</b>. Except this, the construction of the brake mechanism <b>61</b> is similar to those of the first and fourth embodiments.

FIG. 12 is a block diagram showing a shift control of a transmission system according to the sixth embodiment of the present invention. Except that the lock-up clutch <b>51</b> is deleted, other components such as the input clutch <b>53</b>, the bypass clutch <b>18</b>, the brake mechanism <b>61</b> and the hydraulic actuators <b>77</b>, operate in the same manner as in the aforesaid embodiments.

According to this transmission system, since the brake mechanism <b>61</b> is accommodated outside of the outer periphery of the clutch drum <b>54</b> of the input clutch <b>53</b> and provided on the extension member of the flywheel dumper <b>90</b>, the axial size of the transmission can be reduced and the requirement of braking torque can be obtained with compact construction.

FIG. 13 is a skeleton diagram showing a transmission system according to a seventh embodiment. The transmission system comprises the flywheel dumper <b>90</b>, an input clutch <b>53</b>, a brake mechanism <b>61</b>, a plurality of shift gear trains and a bypass clutch <b>18</b> in the same manner as the sixth embodiment. The difference between this embodiment and the sixth embodiment is that the brake system of the sixth embodiment is a disc brake type and on the other hand the brake system of the seventh embodiment is a multiple disc brake type of which construction is the same as that of the second embodiment.

According to this transmission system, since the brake mechanism <b>61</b> is provided around the clutch drum <b>54</b> of the input clutch <b>53</b>, an up-sizing of the transmission in an axial direction in incorporating the brake mechanism <b>61</b> into the transmission can be prevented.

While the present invention has been disclosed in terms of the preferred embodiments in order to facilitate better understanding of the invention, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments which can be embodied without departing from the principle of the invention set out in the appended claims.